Usually, positive type tape-driven yarn feeding devices for circular knitting machines are provided with a plurality of yarn feed wheels driven by an endless drive tape which is driven in timed relationship to operation of the knitting machine. The yarns are fed by guide means in such a manner that they pass through the nip of the drive tape and the yarn feed wheels so as to positively feed the yarn in a continuous manner.
However, this continuous type of yarn feeding device is not adapted for use with knitting machines which require the selective feeding of a plurality of yarns according to variable demands from the knitting machine, such as is required in the operation of stripe and jacquard type circular knitting machines. This continuous type of yarn feeding device is not adaptable to use on stripe and jacquard circular knitting machines because the continuous yarn feeding device is not adaptable to the selective feeding of yarns, according to demand from the knitting machine, and in variable amounts, according to the knit structure.
It is also known to provide yarn feeding devices in which the yarns may be positioned in feeding and nonfeeding positions, depending upon the demand for yarn from the knitting machine. In this type of yarn feeding device the feed wheels are provided with a V-shaped groove and the tension in the yarn changes the position of contact between the yarn and the V-shaped groove in the feed wheel so that the yarn is positively fed when nipped between the tape and the feed wheel and feeding of the yarn is discontinued when the yarn is positioned in the V-shaped groove of the feed wheel. This type of feed device requires a high degree of precision for shaping the groove in the feed wheel and a fairly high degree of tension must be applied to the yarn to cause it to move out of the V-shaped groove and into feeding position on the feed wheel. Also, the range of yarn sizes which may be fed by this type of device is limited by the size and shape of the V-shaped groove and the groove may be easily worn due to contact with the yarn thereby causing expensive replacement of the feed wheels when they become worn.
Japanese patent publication No. 96941/1981 (United Kingdom published Application No. 2 065 723, published July 1, 1981) discloses another type of yarn feeding device which is operable with a stripe knitting machine for selectively feeding the striping yarns thereto. The yarn passes around this yarn feeding device with only a single run of a single wrap of about one hundred and eighty degrees and is provided with yarn guide means for varying the degree of contact between the yarn and the feed wheel so that the yarn assumes either a feeding or a nonfeeding position according to the demand for yarn by the knitting machine. However, tension in the yarn can become extremely high at the time the yarn is moved from the nonfeeding to the feeding position and the tension may become so high as to cause yarn breakage. Additionally, the yarn is not always smoothly transferred from the nonfeeding to the feeding position in accordance with the direction of twist in the yarn (S or Z twist). Furthermore, some types of yarn, such as filament polyester or nylon yarn have a tendency to stick to the frictional surface of the feed wheel and these yarns are difficult to separate from the friction surface when being moved from the feeding to the nonfeeding position so that overfeeding of the yarn may result and the yarn becomes wound around the feed wheel.